Silicone elastomer with unprimed adhesion

ABSTRACT

A COMPOSITION OF A VINYLDIORGANOSILOXY ENDBLOCKED POLYDIMETHYLSILOXANE AND A MIXTURE OF AN ORGANOSILOXANE HAVING 5 TO 20 SILICON ATOMS PER MOLECULE AND AN AVERAGE OF AT LEAST THREE SILICON-BONDED HYDROGEN ATOMS PER MOLECULE AND A MODIFIED ORGANOSILOXANE HAVING 6 TO 21 SILICON ATOMS PER MOLECULE, AN AVERAGE OF AT LEAST TWO SILICON-BONDED HYDROGEN ATOMS PER MOLECULE AND AN AVERAGE OF AT LEAST ONE UNIT OF (RO)3SI(CH2)X(CH3)SIO, (RO)3SI(CH2)X(CH3)2SIO0.5 AND MIXTURES THEREOF WHERE R IS METHYL, ETHYL OR   CH3-CO-   AND X IS 2 OR 3 IS CURABLE TO AN ELASTOMER WHICH HAS IMPROVED UNPRIMED ADHESION TO SUBSTANCES, PARTICULARLY METAL SUBSTRATES.

3,699,072 SILICONE ELASTOMER WITH UNPRIMED ADHESION William H. Clark,Mount Pleasant, and William R. Hays,

Midland, Mich., assignors to Dow Corning Corporation, Midland, Mich. NoDrawing. Filed June 24, 1971, Ser. No. 156,551

Int. Cl. C08g 51/04, 31/02 US. Cl. 260-37 SB 11 Claims ABSTRACT OF THEDISCLOSURE A composition of a vinyldiorganosiloxy endblockedpolydimethylsiloxane and a mixture of an organosiloxane having 5 to 20silicon atoms per molecule and an average of at least threesilicon-bonded hydrogen atoms per molecule and a modified organosiloxanehaving 6 to 21 silicon atoms per molecule, an average of at least twosilicon-bonded hydrogen atoms per molecule and an average of at leastone unit of (RO) Si(CH (CH )SiO, (R) Si(CH ),,(CH SiO and mixturesthereof where R is methyl, ethyl or and x is 2 or 3 is curable to anelastomer which has improved unprimed adhesion to substrates,particularly metal substrates.

This invention relates to an organosiloxane composition which is curableto an elastomer which has improved unprimed adhesion to substrates.

The adhesion of silicone elastomers to substrates, such as metals,glass, paper, wood, masonry, stone and the like is of significantimportance to the spectrum of utility of the silicone elastomer.Although some silicone elastomers adhere to some substrates, not allsilicone elastomers adhere to all substrates. Furthermore, thosesilicone elas tomers which do adhere to some substrates often haveadhesive strengths which limit their utility. One method of gainingimproved adhesion to various substrates is to prime the surface. Thisprocedure although often effective has the disadvantage that the user isrequired to apply two compositions. This is time consuming, inconvenientand in general more expensive. Therefore, to avoid the use of a primer,the elastomer composition can be formulated to provide the necessaryadhesion without the use of primers. The addition of ingredients toelastomer formulations is not without problems, since some ingredientscan destroy the elastomeric properties, inhibit cure and the like. Thecomposition of this invention does not interfere with the elastomer inany way and still provides improved adhesion to substrates.

It is therefore an object of this invention to provide a siloxanecomposition which can be cured to an elastomer having improved unprimedadhesion to substrates. This object and others will become apparent fromthe following detailed description of the present invention.

This invention relates to a curable composition consisting essentiallyof 1) a vinyldiorganosiloxy endblocked polydimethylsiloxane having aviscosity of from 1000 to 100,000 cs. at 25 C. wherein the organicgroups of the vinyldiorganosiloxy units are selected from the groupconsisting of methyl and phenyl, (2) a mixture consisting essentially of(a) an organosiloxane having an average of from 5 to 20 inclusivesilicon atoms per molecule, organosiloxane units bonded together throughsiliconoxygen-silicon bonds and selected from the group consisting ofdimethylsiloxane units and methylhydrogensiloxane units and endblockedwith organosiloxane units United States Patent 0 3,699,072 Patented Oct.17, 1972 ice selected from the group consisting of trimethylsiloxaneunits and dimethylhydrogensiloxane units, there being present an averageof at least three silicon-bonded hydrogen atoms per molecule and (b) amodified organosiloxane having an average of from 6 to 21 silicon atomsper molecule, organosiloxane units bonded together throughsilicon-oxygen-silicon bonds selected from the group consisting ofdimethylsiloxane units, methylhydrogensiloxane units and (RO) Si(CH (CH)SiO units wherein R is a monovalent radical selected from the groupconsisting of methyl, ethyl and O CHJL and x is an integer of from 2 to3 inclusive, and endblocked with organosiloxane units selected from thegroup consisting of trimethylsiloxane units, dimethylhydrogensiloxaneunits and (RO) Si(CH (CH SiO units, there being present an average of atleast two siliconbonded hydrogen atoms per molecule and an average ofone siloxane unit selected from the group consisting of (RO) Si(CH (CH)SiO units and units, said mixture (2) being present in an amountsufficient to provide at least one silicon-bonded hydrogen atom pervinyl radical in (1) and not more than 10 siliconbonded hydrogen atomsper vinyl radical in (1), said mixture having present from 15 to molpercent modified organosiloxane (b) where (a) and (b) are mol percent.

The vinyldiorganosiloxy endblocked polydimethylsiloxanes (1) are wellknown in the art. These polydimethylsiloxanes can have viscosities offrom 1000 to 100,000 cs. at 25 (3., preferably 2000 to 60,000 cs. at 25C. The organic groups of the vinyldiorganosiloxy units can be methyl orphenyl.

The mixture (2) is a crosslinking agent which in the composition of thisinvention, enhances the adhesion of the silicone elastomer to substrateswithout the use of primers. Mixture (2) is a combination of (a) anorganosiloxane having 5 to 20 silicon atoms per molecule and at leastthree silicon-bonded hydrogen atoms and (b) a modified organosiloxanehaving 6 to 21 silicon atoms and at least two silicon-bonded hydrogenatoms and an average of one siloxane unit of the formula OI mixturesthereof. Organosiloxane, (a), contains at least three siliconbondedhydrogen atoms per molecule and from 5 to 20 silicon atoms per molecule.The organosiloxane contains organosiloxane units bonded throughsilicon-oXygen-silicon bonds where the units can be dimethylsiloxaneunits and methylhydrogensiloxane units and endblocking units oftrimethylsiloxane and dimethylhydrogensiloxane. The organosiloxanecontains combinations of the above siloxane units such that there are atleast three silicon-bonded hydrogen atoms per molecule and 5 to 20silicon atoms per molecule. The organosiloxanes (a) can be illustratedby a copolymer containing two units of trimethylsilo-xane, five units ofmethylhydrogensiloxane and three units of dimethylsiloxane, a copolymercontaining two units of dimethylhydrogensiloxane, three units ofmethylhydrogensiloxane and five units of dimethylsiloxane, a copolymerof two units of trimethylsiloxane, seven units of methylhydrogensiloxaneand eleven units of dimethylsiloxane, a copolymer of two units oftrirnethylsiloxane and eighteen units of methylhydrogensiloxane, acopolymer of two units of trimethylsiloxane and three units ofmethylhydrogensiloxane, and a copolymer of two units ofdimethylhydrogensiloxane, ten units of methylhydrogensiloxane and twounits of dimethylsiloxane. The number of siloxane units in thecopolymers are the average number per molecule. The organosiloxanes (a)are well known in the art.

The modified organosiloxanes (b) are the organosilox- 1 anes of (a)wherein some of the silicon-bnded hydrogen atoms have been replaced by(RO) Si(CH R is methyl, ethyl, or

i CHaC- and mixtures thereof. The following copolymers illustrate themodified organosiloxane (b), a copolymer having an average of one unitof one unit of dimethylhydrogensiloxane, four units of dimethylsiloxaneand methylhydrogensiloxane, a copolymer having an average of one unit offive units of dimethylsiloxane, three units of methylhydrogensiloxaneand one unit of dimethylhydrogensiloxane, a copolymer containing anaverage of one unit of (CH3CH20)3SiCH2CH2(CH3)2SiO0 5, one unit ofdimetylhydrogensiloxane and three units of methylhydrogensiloxane, acopolymer containing an average of one unit of Onfi unit ofdimethylhydrogensilox-ane, two units of dimethylsiloxane and two unitsof methylhydrogensiloxane, a copolymer containing an average of twounits of trimethylsiloxane, twounits of methylhydrogensiloxane and oneunit of (CH COO) SiCH CH (CI-I )SiO, a copolymer containing an averageof two units of trimethylsiloxane, one unit of (CH O) SiCH CH (CH )SiO,four units of methylhydrogensiloxane, and three units ofdimethylsiloxane, a copolymer containing an average of two units ofdimethylhydrogensiloxane, one unit of (CH CH O) SiCH CH CH (CH SiO twounits of methylhydrogensiloxane and five units of dimethylsiloxane and amixture of a copolymer containing an average of one unit of(CH3COO)3SiCH2CH2(CH3)2SlO0 5 three units of methylhydrogensiloxane,five units of dimethylsiloxane and one unit of dimethylhydrogensiloxaneand a copolymer containing an average of two units ofdimethylhydrogensiloxane, two units of methylhydrogensiloxane, one unitof (CH COO') SiCH CH (CH )SiO and five units of dimethylsiloxane. Theremay be some molecules of organosiloxane (b) which have two units of theadduct. However, since the ratio of organsiloxane containing thesilicon-bonded hydrogen atoms to silane is in favor of only oneadductper molecule, there will not be large amounts of such molecules. Themixture of (a) and (b) can include such amounts of molecules with twoadducts without departing from the scope of this invention.

Mixture (2) can be prepared by reacting part of the organosiloxanecontaining silicon-bonded hydrogen atoms with a silane suchasvinyltriacetoxysilane, allyltrimethoxysilane, vinyltriethoxysilane,vinyltrimethoxysilane, allyltriacetoxysilane and allyltriethoxysilane.The amount 4 of silane used is sufficient to provide 15 to 75 molpercent of modified organosiloxane (b) with the remainder unreactedorganosiloxane as defined in (a) and the mixture of (a) and (b) is molpercent. The reaction is best carried out by heating a mixture oforganosiloxane having silicon-bonded hydrogen atoms and the silane for 1to 2 hours at C. to C. The reaction can be carried out at lowertemperatures and in shorter periods of time by heating the reactionmixture in the presence of a platinum in preparing the mixture (2) isnot preferred when the composition of this invention is to be stored forlong periods of time, since the residual platinum catalyst from thepreparation of mixture 2) will cause the composition to cure. When aplatinum catalyst is used to prepare the mixture and storage of thecomposition is desired, the

platinum catalyst should be removed by careful filtration,

such as mixing with charcoal and then filtering. However, the platinumneed not be removed and the mixture (2) can be added to thevinyldiorganosiloxy endblocked polydimethylsiloxane at the time cure isdesired.

The platinum catalyst need not be removed if the composition is to becured above room temperature, such as above 50 C. to 70 C. Where a heatcure is desired, the platinum catalyst composition can contain aninhibitor which inhibits cure at room temperature and up to about 50 C.,however, the composition cures when heated above 50 C. Such inhibitorsinclude benzotriazole, stannous salts, mercuric salts, bismuth salts,cuprous salts, cupric salts, acetylenic unsaturated compounds such as2-ethynylisopropanol and the like.

The composition of this invention can be prepared by mixing thevinyldiorganosiloxy endblocked polydimethylsiloxane with mixture (2)such that there is at least one silicon-bonded hydrogen atom per vinylradical of the vinyldiorganosiloxy endblocked polydimethylsiloxane. Theamount of mixture (2) can be suflicient enough to provide up to tensilicon-bonded hydrogen atoms per vinyl radical of (1) or more. Thehigher ratio of silicon bonded hydrogen atoms to vinyl radical ispreferably used when the composition of this invention has a fillerpresent.

The compositions of this invention can be cured by adding a platinumcatalyst. The platinum catalyst can be present in catalytic amounts suchas 0.5 to 200 parts by weight of platinum per million parts by weight ofvinyldiorganosiloxy endblocked polydimethylsiloxane, preferably from 1to 50 parts by weight of platinum per million parts by weight of thepolydimethylsiloxane.

The platinum catalysts are Well known and any of the platinum catalystswhich are readily dispersible in the composition of this invention aresuitable. The platinum catalysts can be illustrated by platinicchloride, salts of platinum, platinum complexes and chloroplatinic acid,such as PtCl {P(CH CH CH platinum bromides, a complex of platinoushalide and an olefin such as ethylene, Pt(CH CN) 01 {Pt(CH CN) (CH }ClPt(NI-I C1 K{PtCl CH CH CH OH}, PtBr (C 'H K{PtBr3 (C2114) PtC12(C2H4),)2C;CH2 PtCI PtCl CO and PtBr CO.

The composition of this invention can also contain fillers. The fillersare those conventionally used in silicon elastomers either reinforcingsuch as fume silica or nonreinforcing. The silica fillers can be treatedor untreated to make them hydrophobic. Treated fillers are well known inthe art and include treatment with chlorosilanes, such astriorganochlorosilanes and diorganodichlorosilanes,diorganocyclosiloxanes, hexaorganodisiloxane, organesilazanes and thelike. Examples of suitable fillers include, fume silica, silica aerogel,silica xerogel, silica soot, carbon black, quartz, diatomaceous earth,metal carbonates such as calcium carbonate, metal oxides, such asalumina, metal silicates such 'as zirconium silicate, clays, talc andthe like. The amount of filler can vary broadly from no filler toamounts such as 200 parts by weight per 100 parts by weight ofcomposition depending upon the filler and the properties desired.

The compositions of this invention can also contain other ingredientsconventionally used in silicone elastomers such as pigments and dyes toimpart color, plasticizers, heat stability additives and the like.

The compositions of this invention can be prepared by mixing theingredients by conventional means, such as milling, commercial mixersand the like. The order of mixing is not narrowly critical, however, oneconvenient method is to use the base polymer, in this case thevinyldiorganosiloxy endblocked polydimethylsiloxane, and the otheringredients are added to it such as filler, if used,

the platinum catalyst and then when cure is desired mixture (2) isadded.

The compositions of this invention are particularly useful aselastomers, potting compounds, coatings, electrical insulation and otheruses where silicone elastomers find utility. The compositions of thisinvention have an advantage over prior art silicone elastomers in thatthe composition when cured in contact with a substrate the curedsilicone elastomer has improved adhesion to unprimed surfaces.Composites of silicone elastomers and metal substrates can be obtainedby applying the composition of this invention with a platinum catalystand thereafter curing the elastomer by heating above 80 C. for at leastMixture (A) contained modified organosiloxane molecules having anaverage of one unit of (CH COO) SiCH CH (CH SiO per molecule and theamount of modified organosiloxane in the mixture was 28 mol percentwhere the unreacted copolymer defined in (A) made up the remainder.Mixture (B) contained modified organosiloxane molecules having anaverage of one unit of (CH O) SiCH CH CH (CH SiO per molecule and theamount of modified organosiloxane in the mixture was 56 mol percentwhere the unreacted copolymer defined in (A) made up the remainder.Mixture (C) contained modified organosiloxane having an average of oneunit of (CH CH O*) SiCH CH (CH )SiO per molecule and the amount ofmodified organosiloxane in the mixture was 48 mol percent where theunreacted copolymer defined in (A) made up the remainder.

The silicone elastomer composition was prepared by mixing in acommercial mixer 100 parts by weight of a methylphenylvinylsiloxyendblocked polydimethylsiloxane having a viscosity of 15,000 cs. at 25C., 30 parts by weight of a fume silica filler hydrophobed bytrimethylsiloxy groups, 2.5 parts by Weight of mixture (A), (B) or (C)as defined above, and 20 drops of a chloroplatinic acid catalyst. Thesilicone elastomer composition was cured in test bars for physicalproperty measurements and was also cured on aluminum and steel panelsfor adhesion measurements in accordance with ASTM-D-903 procedure, 180peel strength. The compositions were cured for TABLE I Adhesion AluminumSteel Tensile Elonga- Tear Cure Duromstrength tion at strength PeelPercent Peel Percent Composition with conditions, eter, at break, break,Die B strength, cohesive strength, cohesive mixture 0. Shore A 0.s.i.percent p.p.i. p.l.i. failure p.l.r failure Control 1 RIP. 28 1 110 88772 8 0 12.2 0 D0 150 30 1: 080 827 48 25 0 90 (A). R11. 32 880 807 84 450 a0 0 (A)- 150 31 1, 180 900 74 122 100 122 100 R.T. 28 1,190 920 64 24O 20 0 R.T. 27 1, 240 91a 65 24 0 1e 0 1 Control was 2.5 parts by weightof the copolymer as defined in (A) above.

2 Room Temperature.

5 minutes. Although the silicone elastomer cures at room temperature,heating the composite enhances the adhesion to the metal substrate. Theimproved adhesion is particularly enhanced where the substrate is ametal such as aluminum or steel.

The following examples are illustrative only and should not be construedas limiting this invention which is properly delineated in the claims.

EXAMPLE 1 The following mixtures were prepared by reacting theingredients defined below by heating 1.5 hours at 150 C.

30 parts by weight of a copolymer containing an average of twotrimethylsiloxane units, three dimethylsiloxaue units and fivemethylhydrogensiloxane units and 2.9 parts by weightvinyltriacetoxysilane 30 parts by weight of the copolymer defined in (A)above and 4.0 parts by weight allyltrimethoxysilane 30 parts by weightof the copolymer defined in (A) above and 4.0 parts by weight ofvinyltriethoxysilane.

15 minutes at 150 C. and also for one week at room temperature. Theresults were as shown in Table I.

On samples of the room temperature cured silicone elastomer compositionsthe adhesion was determined after one year. The control on steel had apeel strength of 24 p.l.i. with no cohesive failure and on aluminum hada peel strength of 5 p.l.i. with no cohesive failure. The siliconeelastomer with mixture (A) on steel had a peel strength of 66 p.l.i.with 10 percent cohesive failure and on aluminum had a peel strength ofp.l.i. with percent cohesive failure. The silicone elastomer withmixture (C) on steel had a peel strength of 30 p.l.i. with no cohesivefailure and on aluminum had a peel strength of 90 p.l.i. with 100percent cohesive failure.

EXAMPLE 2 The following mixtures were prepared by reacting 30 parts byweight of the copolymer defined in Example 1, (A) with an amount ofsilane as shown in Table II by heating for 1.5 hours at C. The molpercentage of modified organosiloxane and the adduct unit present in anaverage of one unit per molecule of modified organosiloxane was as shownin Table II. In each case the remaining mol percentage was unreactedcopolymer as defined in Example 1, (A).

TABLE II Mol Amount percent of of silane, modified parts by organoMixture Silane weight Adduct unit siloxane (A)Allyltrimethoxysilane-..-- 2.9 (CHsOhSiCHzCHzCH:(CH3)S1O 41 (B)Vinyltriethoxysilane- 2. 9 (CH;CH1O);S1CH1CH1(CH=) S10 35 (C)Vinyltriaeetoxysilane-. 2. (@1130 O O);SiCH1OHz (CH1) SiO 19 (D).--Allyltrimethoxysilane. 2.0 (CHaO):SiCH2CHzCH2(CHa)S10 28 (E)-Vinyltriethoxysilane- 2. 0 (CH CH1O);4SiCH2CHr(CHa) SiO 24 (F)Vinyltriacetoxysilane 4. 0 (CHaCOO)3SiCH:CH2(CH3)S10 39 (G) (ln 5. 0(CHaCOO)aSiCH2CH2(CH )SiO 49 (H) Allyltrimethoxysiiane.--.- 5.0(CHaO)3SiCHaCHrCHn(OHs)S10 70 (I)..- Vin yltriethoxysilane 5. 0(CH3CH2O)3S1CH2CH2(CH3) S 60 The silicone elastomer compositions wereprepared by The silicone elastomer compositions as described inExammixing on a commercial mixer 100 parts by weight of pie 1 wereprepared with the above mixtures (A) through (I) and the physicalproperties and adhesion properties were determined as described inExample 1. The silicone elastomers in this example were all cured forminutes at 150 C. The results were as shown in Table III.

a methylphenylvinylsiloxy endblocked polydimethylsiloxane having aviscosity of 58,000 cs. at C., 20 parts by weight of a fume silica asdefined in Example 1, 1.5 parts by weight of a mixture of (A) through(E) as de- TABLE III Adhesion Aluminum Steel Tensile Elonga- TearDuromstrength tion at strength Peel Percent Peel Percent Compositioneter, at break, break, Die B, strength, cohesive strength, cohesive withmixture Shore A p.s.i. percent p.p.i. p.l.1 failure p.1.i failureControl 1 1, 080 827 48 25 0 90 27 1, 316 960 90 50 90 50 29 1, 086 92049 85 50 85 50 1 Control was 2.5 parts by weight of the copolymer asdefined in (A) above.

EXAMPLE 3 35 fined above and 20 drops of a chloroplatinic acid catalyst.The silicone elastomer was cured for testing both for physicalproperties and adhesion tested by heating 15 minutes at 150 C. Theadhesion tests were carried out the same as in Example 1. The resultswere as shown in The following mixtures were prepared by reacting 30parts by weight of the copolymer as defined in Example 1, (A), 2.9 partsby weight of the silanes shown in Table IV and a catalytic amount of achloroplatinic acid catalyst by heating for one hour at 100 C. The molper- 40 Table TABLE V Adhesion Aluminum Steel Tensile Elonga- TearDuromstrength tion at strength Peel Percent Peel Percent Compositioneter, at break, break, Die B, strength, cohesive strength, cohesive withmixture Shore A p.s.i. percent p.p.i. p.l.i. failure p.l.i. failurecentage of modified organosiloxane present in the re- That which isclaimed is:

acted mixture was as shown in Table IV with the remaining molpercentagebeing the unreacted copolymer as defined in Example 1. Themodified organosiloxane contained an average of one adduct unit permolecule, the adduct unit corresponding to the silane and present inratio as the silane was added. The adduct units were as shown in TableIV.

1. A curable composition consisting essentially of (1) avinyldiorganosiloxy endblocked polydimethylsiloxane having a viscosityof from 1000 to 100,000 cs. at 25 C.

wherein the organic groups of the vinyldiorganosiloxyunits are selectedfrom the group consisting of methyl and phenyl, (2) a mixture consistingessentially of (a) an organosiloxane having an average of from 5 to 20inclu- TABLE IV Mol Amount percent of of silane, modified parts byorgane- Mixture Silane weight Adduct unit siloxane (A)Vinyltriacetoxysilane 2.9 (CHaCOO)3SiCHlCH2(CHa)SiO 28 (B){Vinytriacetoxysilane 2. 0 (CH;CO 0) aSiCHzCH1(CH:) S10 32Allyltriacetoxysilane-.. 0.9 (CH30)rSiCH:CH2CH1(CHs)SiO (C){Vinytriacetoxysilane 1. 45 (CHsC O O):S1CH1CH2(CH:) S10 36Allyltriacetoxysilane. 1. 45 (CHaOhSiCHzCHflH, (CH3) SiO (D){Vinytriacetoxysilane 0. 9 (CH;C OO)zSiCHzCHa(CH:) SiO 37Allyltrimethoxysilane. 2. 0 (CH30)3S1OHICH2CH2(OHJ) S10 (E)Allyltrimethoxysilane 2.9 (CH;0)|SiCH1CH1CH;(CH:)SiO 41 units wherein Ris a monovalent radical selected from the group consisting of methyl,ethyl and and x is an integer of from 2 to 3 inclusive, and endblockedwith organosiloxane units selected from the group consisting oftrimethylsiloxane units, dimethylhydrogensiloxane units and (RO) Si(CH(CH SiO units, there being present an average of at least twosiliconbonded hydrogen atoms per molecule and an average of one siloxaneunit selected from the group consisting of (RO) Si(CH (CH )SiO units andunits, said mixture (2) being present in an amount suflicient to provideat least one silicon-bonded hydrogen atom per vinyl radical in (1) andnot more than silicon-bonded hydrogen atoms per vinyl radical in (1),said mixture having present from to 75 mol percent modifiedorganosiloxane (b) where (a) and (b) are 100 mol percent.

2. The composition in accordance with claim 1 in which the endblockingunit of (1) is methylphenylvinylsiloxy, the viscosity of (1) is from2000 to 60,000 cs. at C., R is O CHA- andxis 2.

3. The composition in accordance with claim 1 in which the endblockingunit of (1) is methylphenylvinylsiloxy, the viscosity of (1) is from2000 to 60,000 cs. at 25 C., R is methyl and x is 3.

4. The composition in accordance with claim 1 in which the endblockingunit of (1) is methylphenylvinylsiloxy, the viscosity of (1) is from2000 to 60,000 cs. at 25 C., R is ethyl and x is 2.

5. The composition in accordance with claim 1 in which the endblockingunit of (1) is methylphenylvinylsiloxy, the viscosity of (1) is from2000 ot 60,000 cs. at 25 C., some R groups are and the remainder of theR groups are methyl and where R is x is 2 and where R is methyl, x is 3.

6. The composition in accordance with claim 1 in which a filler ispresent.

7. The composition in accordance with claim 6 in which the filler is areinforcing silica filler.

8. The composition in accordance with claim 2 in which a filler ispresent.

9. The composition in accordance with claim 3 in which a filler ispresent.

10. The composition in accordance with claim 4 in which a filler ispresent.

11. The composition in accordance with claim 5 in which a filler ispresent.

References Cited UNITED STATES PATENTS 3,527,655 9/1970 Ballard 260-465UA 3,647,917 3/1972 Schulz et al. 260-465 G X LEWIS T. JACOBS, PrimaryExaminer 11.8. C1. X.R.

260-465 G, 46.5 UA

